# STINGS
```
Description
Enter the beehive. Don't get stung.

(Note: the password/flag is in the format ictf{.*})

Attachments
https://2021.imaginaryctf.org/r/stings

```

- File : [stings](https://github.com/Pynard/writeups/blob/main/2021/IMAGINARYCTF/attachements/stings/stings?raw=true)

Here we have to type the password that is the flag

Looking in gdb we can see that the typed pwd is compared with an other string from which each is char is substracted by 1 :
```
│ ┌─< 0x0000083c eb47 jmp 0x885
│ │ ; CODE XREF from main @ 0x88c
│ ┌──> 0x0000083e 8b85ecedffff mov eax, dword [var_1214h]
│ ╎│ 0x00000844 4898 cdqe
│ ╎│ 0x00000846 0fb68405f0ed. movzx eax, byte [rbp + rax - 0x1210]
│ ╎│ 0x0000084e 0fbed0 movsx edx, al
│ ╎│ 0x00000851 8b85ecedffff mov eax, dword [var_1214h]
│ ╎│ 0x00000857 4898 cdqe
│ ╎│ 0x00000859 0fb68405f0ee. movzx eax, byte [rbp + rax - 0x1110]
│ ╎│ 0x00000861 0fbec0 movsx eax, al
│ ╎│ 0x00000864 83e801 sub eax, 1
│ ╎│ 0x00000867 39c2 cmp edx, eax
│ ┌───< 0x00000869 7413 je 0x87e
│ │╎│ 0x0000086b 488d3d1e0100. lea rdi, str.Im_disappointed._stings_you ; 0x990 ; "I'm disappointed. *stings you*"
│ │╎│ 0x00000872 e859fdffff call sym.imp.puts
│ │╎│ 0x00000877 b8ffffffff mov eax, 0xffffffff ; -1
│ ┌────< 0x0000087c eb21 jmp 0x89f
│ ││╎│ ; CODE XREF from main @ 0x869
│ │└───> 0x0000087e 8385ecedffff. add dword [var_1214h], 1
│ │ ╎│ ; CODE XREF from main @ 0x83c
│ │ ╎└─> 0x00000885 83bdecedffff. cmp dword [var_1214h], 0x22
│ │ └──< 0x0000088c 7eb0 jle 0x83e
│ │ 0x0000088e 488d3d1b0100. lea rdi, str.Congrats__The_password_is_the_flag. ; 0x9b0 ; "Congrats! The password is the flag."
│ │ 0x00000895 e836fdffff call sym.imp.puts
```

At each loop from **0x0000088c** to **0x0000083e** we need to take the jump at **0x00000869**

The current character tested is subtracted by 1 at **0x00000864**

With radare 2, here are the strings compared with the type pwd :
```
│ 0x00000779 4889d7 mov rdi, rdx
│ 0x0000077c f348ab rep stosq qword [rdi], rax
│ 0x0000077f 48b86a647567. movabs rax, 0x7375747c6775646a ; 'jdug|tus'
│ 0x00000789 48ba326f6874. movabs rdx, 0x3473356074686f32 ; '2oht`5s4'
│ 0x00000793 488985f0eeff. mov qword [var_1110h], rax
│ 0x0000079a 488995f8eeff. mov qword [var_1108h], rdx
│ 0x000007a1 48b86f756069. movabs rax, 0x346565326960756f ; 'ou`i2ee4'
│ 0x000007ab 48ba6f603238. movabs rdx, 0x623233633832606f ; 'o`28c32b'
│ 0x000007b5 48898500efff. mov qword [var_1100h], rax
│ 0x000007bc 48899508efff. mov qword [var_10f8h], rdx
│ 0x000007c3 48c78510efff. mov qword [var_10f0h], 0x7e3a37 ; '7:~'
│ 0x000007ce 48c78518efff. mov qword [var_10e8h], 0
│ 0x000007d9 488d9520efff. lea rdx, [var_10e0h]
```

A simple python script to solve the flag :

```py
flag = 'jdug|tus2oht`5s4ou`i2ee4o`28c32b7:~'
''.join([ chr(ord(elt)-1) for elt in flag ])
```

it gives us :
```
ictf{str1ngs_4r3nt_h1dd3n_17b21a69}
```

flag : `ictf{str1ngs_4r3nt_h1dd3n_17b21a69}`

Original writeup (https://github.com/Pynard/writeups/blob/main/2021/IMAGINARYCTF/challenges/stings.md).